This invention relates to a method and apparatus for the improved manufacture of cement in wet or dry process long rotary kilns, or in preheater kilns, for processing a mineral material therein to produce cement clinker. More particularly this invention is directed to improvements in the operation and configuration of long rotary cement kilns to permit burning of a bulk material supplemental fuel in a secondary burning zone of the kiln.
In the widely used commercial process for the manufacture of cement, the steps of drying, calcining, and clinkering cement raw materials are accomplished by passing finely divided raw materials, including calcareous minerals, silica and alumina, through a heated, inclined rotary vessel or kiln. In what is known as conventional long dry or wet process kilns the entire mineral heating process is conducted in a heated rotating kiln cylinder, commonly referred to as a "rotary vessel". The rotary vessel is typically 10 to 15 feet in diameter and 400-700 feet in length and is inclined so that as the vessel is rotated, raw materials fed into the upper end of the kiln cylinder move under the influence of gravity toward the lower "fired" end where the final clinkering process takes place and where the product cement clinker is discharged for cooling and subsequent processing. Kiln gas temperatures in the fired clinkering zone of the kiln range from about 1300.degree. to about 1600.degree. C. Kiln gas temperatures are as low as about 250.degree. to 350.degree. C. at the upper mineral receiving end of so-called wet process kilns. Somewhat higher kiln gas temperatures exist in the upper end of long dry process kilns.
Generally, skilled practitioners consider the cement making process within the rotary kiln to occur in several stages as the raw material flows from the cooler gas exit mineral feed end to the fired/clinker exit lower end of the rotary kiln vessel. As the mineral material moves down the length of the kiln it is subjected to increasing kiln gas temperatures. Thus in the upper portion of the kiln cylinder where the kiln gas temperatures are the lowest, the in-process mineral materials first undergo a drying process and thereafter move down the kiln cylinder until the temperature is raised to calcining temperature. The length of the kiln where the mineral is undergoing a calcining process (releasing carbon dioxide) is designated the calcining zone. The in-process mineral finally moves down the kiln where the kiln into a zone where gas temperatures are the hottest, the clinkering zone adjacent the fired lower end of the kiln cylinder. The drying zone, the calcining zone, and the clinkering zone typically are not contiguous lengths along the kiln cylinder. The kiln gas stream flows counter to the flow of in-process mineral materials from the clinkering zone, through the intermediate calcining zone and the mineral drying zone and out the upper gas exit end of the kiln into a kiln dust collection system. The flow of kiln gases through the kiln can be controlled to some extent by a draft induction fan positioned in the kiln gas exhaust stream.
Cement kilns have received favorable review from both federal and state environmental regulatory agencies for disposal of both liquid and solid combustible waste materials. Cement kilns provide a combination of high operating temperatures and long residence times, both of which are favorable conditions for complete combustion of organic components of waste and chemical combination of inorganic components with the reactive in-process mineral components. Combustible waste solids provide a source of inexpensive energy for the mineral processing industry.
For many years, regulation compliant use and disposal of waste in operating kilns was limited to combustible liquid or "pumpable" hazardous waste. Liquid waste materials are easily blended with each other and with conventional fuels to provide homogeneous liquids that can be burned in the gaseous phase at the firing end of the kiln with little or no modification of kiln burner configuration. Solid waste derived fuel, however, can occur in multiplicity of forms, from hard crystalline solids to viscous, sticky sludges. They are not easily blended, and they present significant engineering challenges for their safe handling and delivery into rotating kilns.
Several apparatus have been designed to facilitate firing of solid wastes into kilns. See, for example, U.S. Pat. No. 4,850,290, issued Jul. 25, 1989; U.S. Pat. No. 4,930,965, issued Jun. 5, 1990; U.S. Pat. No. 4,974,529, issued Dec. 4, 1990; and U.S. Pat. No. 5,083,516 issued Jan. 7, 1992; incorporated herein by reference. These four patents describe an apparatus and method for delivering containerized waste to both pre-heater type and conventional long wet or dry kilns at the point in the process where the kiln gas temperature is such that volatilized components are consumed with high destruction and removal efficiency. The above-cited patents describe a device for delivering containerized waste through the wall of a kiln cylinder during kiln operation. The apparatus comprises a fuel charging port, preferably with a mechanical closure, formed in the kiln cylinder wall. The fuel charging port is aligned with a drop tube inside the kiln cylinder. The drop tube prevents hot in-process mineral material in the kiln from escaping through the fuel charging port or contacting closure. The device is utilized to deliver containerized waste into a secondary burning zone of the kiln at predetermined time during kiln cylinder rotation.
Other apparatus and methods for delivering solid fuels, especially solid waste derived fuels, are known in the art. See, for example, U.S. Pat. No. 5,078,594, issued Jan. 7, 1992. The '594 patent discloses a charging apparatus for delivering tires or other combustible waste solids through a port into a rotating kiln. U.S. Pat. No. 5,339,751 owned by the assignees of the present invention discloses a waste derived fuel delivery control method and apparatus capable of charging more than one container or other type of solid waste fuel into the kiln for each revolution of the kiln. In addition, containerized solid waste derived fuel can be fired from an industrial cannon mounted at the lower fired end of the kiln into the secondary burning zone of the kiln. See U.S. Pat. Nos. 5,086,716 and 4,984,983 for examples of industrial cannon fuel delivery systems.
Packaging the solid waste derived fuel into suitable containers for charging into the kiln adds a significant amount to the cost of delivering supplemental fuel to the kiln. Substantial cost savings are obtained by charging the bulk material directly into the kiln without first placing the bulk material into containers.
Attempts have been made to deliver an uncontainerized bulk material supplemental fuel to a kiln. U.S. Pat. No. 5,257,586 discloses one such supplemental fuel delivery apparatus. The '586 patent discloses a feed mechanism including an auger screw which rotates with the kiln. The feed mechanism of the '586 patent scoops up material from a transfer drum during rotation of the kiln and the auger screw forces the material into the kiln through a discharge tube. A feed hopper including a knife gate and a hydraulic ram may also be used to load an inlet of the feeding mechanism disclosed in the '586 patent.
One object of the present invention is to provide an improved bulk material charging apparatus to facilitate charging of bulk fuel material directly into a rotating kiln without the need for containerizing the bulk material, thereby substantially reducing packaging costs associated with delivering a supplemental fuel into the rotating kiln.
The apparatus and method of the present invention provides an improvement for handling bulk materials on site at the kiln and for charging the bulk material directly into the kiln. The present apparatus and method facilitates handling of the bulk material. The apparatus is designed to have minimal interference on the physical operation of the kiln. The apparatus advantageously permits bulk feeding of a supplemental fuel, such as a solid waste derived fuel (SWDF), into the rotary vessel of the kiln using conventional mechanical equipment.
Burning a supplemental fuel, either a natural fossil fuel such as lump coal or a waste derived fuel, charged into the kiln reduces fuel consumption of the burner at the lower fired end of the kiln. Environmentally sound burning requires complete combustion of the supplemental fuel. The goal is to optimize combustion conditions to minimize discharge of carbon monoxide and other products of incomplete combustion into the atmosphere. Carbon monoxide is produced as a result of incomplete combustion. Optimal combustion conditions also reduce discharge of organic residues from waste derived fuels from the lower fired end of the kiln in the clinker.
Another object of the present invention is to improve combustion efficiency within a secondary burning zone of the kiln by providing multiple fuel charges for each revolution of the rotary vessel and by providing high velocity tertiary or mixing air with each fuel charge into the secondary burning zone.
It is understood that the bulk material supplemental fuel charging apparatus of the present invention can be used along with a conventional charging apparatus for charging containerized solid waste derived fuel into the rotary vessel. The use of the combination of the present invention with the conventional containerized fuel charging apparatus would reduce the amount of containerized supplemental fuel required and thereby still substantially reduce packaging costs associated with delivering such supplemental fuel to the kiln.
According to one aspect of the present invention, an apparatus is provided for improved manufacture of cement clinker in a wet or dry process long rotary kiln for processing a mineral material therein to produce cement clinker. The kiln includes a rotary vessel having a fired lower end and an adjacent clinkering zone, an upper kiln gas exit end and an adjacent mineral drying zone, an intermediate calcining zone along its length, and a kiln gas stream flowing from the fired lower end to the upper gas exit end. The kiln is modified to burn a bulk material supplemental fuel in a secondary burning zone of the kiln. The apparatus of the present invention includes a port formed in the rotary vessel upstream relative to kiln gas flow of the drying zone, a tube extending into the rotary vessel in communication with the port to prevent an in-process mineral material in the rotary vessel from escaping through the port, and a bulk material fuel charging apparatus. The charging apparatus includes a hopper for receiving the bulk material, a barrel in communication with the hopper, a cylinder having a piston for moving a ram located within the hopper from a retracted position to an extended position to load a portion of the bulk material into the barrel and form a fuel charge, and an air cannon in air flow communication with the barrel for injecting air into the barrel to force the fuel charge out of the barrel, through the tube, and into an interior region of the rotary vessel.
In the illustrated embodiment, the apparatus also includes a compaction cylinder coupled to the charging apparatus. The compaction cylinder includes a piston and a compaction ram coupled to the piston. The compaction ram is located inside the hopper for compacting the bulk material in the hopper as the compaction ram is moved from a retracted position to an extended position by the compaction cylinder.
Also in the illustrated embodiment, the apparatus includes a stationary annular plenum surrounding rotary vessel. The plenum is configured to define an enclosed interior region in communication with a discharge end of the barrel of the charging apparatus and with the port in the rotary vessel. A storage container is located adjacent the kiln for storing the bulk material, and a conveyor is provided for transporting the bulk material from the storage container to the hopper of the fuel charging apparatus. A second conveyor is also provided for transporting bulk material from inside the annular plenum to the storage container for reloading back into the hopper of the charging apparatus.
A fan is coupled to the annular plenum and a filter is coupled to the fan. The fan withdraws air from the interior region of the annular plenum through the filter. Illustratively, the filter is an activated carbon filter.
The apparatus further includes a target plate coupled to the rotary vessel and a sensor for detecting a position of the target plate. The sensor activates the air cannon when the tube is aligned with the barrel of the charging apparatus. A valve is preferably coupled to the tube for selectively opening and closing the tube to permit the fuel charge to pass through the tube and into the interior region of the rotary vessel.
Optionally, the apparatus may include a second bulk material fuel charging apparatus for charging another fuel charge through the tube during rotation of the rotary vessel. The apparatus may also include a second port formed in the rotary vessel angularly spaced from the first port, and a second tube extending into the rotary vessel in communication with the second port to provide a second fuel delivery tube for the first and second bulk material fuel charging apparatus. Illustratively, the second bulk material fuel charging apparatus includes a second hopper for receiving the bulk material, a second barrel in communication with the second hopper, a second cylinder having a piston for moving a ram located within the second hopper from a retracted position to an extended position to load a portion of the bulk material into the second barrel and form a fuel charge, and a second air cannon in air flow communication with the second barrel for injecting air into the second barrel to force the fuel charge out of the second barrel, through the tube, and into the interior region of the rotary vessel.
The barrel of the fuel charging apparatus includes an open discharge end. The barrel is preferably angled upwardly to prevent the bulk material from exiting the barrel and hopper through the open discharge end of the barrel. The barrel has a predetermined diameter which is smaller than a diameter of the tube.
According to another aspect of the present invention, an apparatus is provided for feeding a bulk material supplemental fuel through a port formed in a side wall of a rotary vessel of a cement kiln. The apparatus includes a stationary annular plenum surrounding rotary vessel. The plenum is configured to define an enclosed interior region in communication with the port in the rotary vessel. The apparatus also includes a bulk material fuel charging apparatus including a hopper for receiving the bulk material, and a barrel in communication with the hopper. The barrel has an open discharge end extending into the interior region of the annular plenum. The bulk material fuel charging apparatus also includes an air cannon in air flow communication with the barrel for injecting air into the barrel to force a portion of the bulk material located in the barrel out of the open discharge end of the barrel, through the port, and into the rotary vessel.
In the illustrated embodiment, the charging apparatus includes a chambering cylinder coupled to the hopper. The cylinder controls a piston to move a chambering ram located within the hopper from a retracted position to an extended position to load the portion of the bulk material from the hopper into the barrel to form a fuel charge. The apparatus also includes a compaction cylinder coupled to the charging apparatus. The compaction cylinder includes a piston and a compaction ram coupled to the piston. The compaction ram is located inside the hopper for compacting the bulk material in the hopper as the compaction ram is moved from a retracted position to an extended position by the compaction cylinder.
According to yet another aspect of the present invention, a method is provided for improving the manufacture of cement clinker in a conventional long rotary cement kiln comprising a rotary vessel having an upper kiln gas exit end with an adjacent mineral drying zone, and opposite fired clinker exit end with an adjacent clinkering zone and an intermediate mineral calcining zone. During operation, a kiln gas stream flows from said clinkering zone through the calcining zone and out the kiln gas exit end of the rotary vessel. An in-process mineral flows from the drying zone through the clinkering zone. The method includes the steps of forming a port in the rotary vessel at a predetermined location along a longitudinal axis of the rotary vessel upstream relative to kiln gas flow of the drying zone, positioning a barrel of a bulk material fuel charging apparatus at said predetermined location aligned with the port, loading a bulk material into the barrel to form a fuel charge, and supplying high pressure air to the barrel when the port is aligned with the barrel to eject the fuel charge from the barrel, through the port, and into an interior region of the rotary vessel.
In the illustrated method, the loading step includes the steps of loading the bulk material into a hopper in communication with the barrel, compacting the bulk material inside the hopper, and forcing a portion of the bulk material from the hopper and into the barrel to form the fuel charge. The method also includes the step of detecting when the port is aligned with the barrel to control timing of the air supplying step.
The illustrated method further includes the step of forming an enclosed air chamber surrounding rotary vessel. The enclosed air chamber is in communication with a discharge end of the barrel and with the port formed in the rotary vessel. The method still further includes the step of withdrawing air from the enclosed air chamber through a filter.
Additional objects, features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.